This application relates generally to turbochargers for internal combustion engines.
Exhaust gas-driven turbochargers employ a turbine to extract power from the stream of exhaust gas coming from an internal combustion engine and use that power to drive a compressor in order to boost the pressure of the air supplied to the cylinders. Single-stage centrifugal compressors are often designed to produce peak pressure ratios of 4.0 or more. In some applications, however, higher pressure ratios are desired, in which case it is common to employ two-stage serial compressors. A two-stage serial compressor has two impellers mounted on the same shaft, sometimes in a back-to-back configuration. Air pressurized by the first-stage impeller is routed to the inlet of the second-stage impeller, where the air is further pressurized and then supplied to the intake manifold of the engine. Using this technique, peak pressure ratios of 7.0 or more can be achieved.
One drawback of two-stage serial compressors is that at operating conditions having relatively high flow rates but low pressure ratios, the efficiency of the compressor falls off dramatically.